1. Field of the Invention
The present invention relates to a method of manufacturing a semiconductor device and a method of processing a substrate, the methods including a process of forming a thin film on a substrate, and a substrate processing apparatus suitable for the process.
2. Description of the Related Art
A flash memory includes an electron accumulation region (floating gate) surrounded by an insulating film and operates in a manner such that information is written in the flash memory by electron exchange through a thin tunnel oxide film and the stored information is retained for a long time by holding electrons using the insulating capacity of the thin tunnel oxide film. Information is stored by accumulating electrons or holes into the floating gate through a tunnel insulating film upon writing and erasure in the flash memory. However, as miniaturization is performed, an equivalent oxide thickness (EOT, an oxide film-converted film thickness) of the tunnel insulating film must be decreased. Accordingly, a nitride film (Si3N4 film, hereinafter, referred to as a SiN film) having a higher permittivity than an oxide film (SiO2 film, hereinafter, referred to as a SiO film) may be used as the tunnel insulating film. However, since the SiN film has a high defect density, a reduction in defect density is needed. Since structural defects such as a dangling bond are easily bonded to hydrogen, a film in which a large number of hydrogen atoms are contained may be referred to as a film having a high defect density. Accordingly, a high quality SiN film with no hydrogen is needed.
In the related art, the SiN film is formed by, for example, a chemical vapor deposition (CVD) method using SiH2Cl2 gas and NH3 gas at a high temperature of about 700 to 800° C. However, since the SiN film formed by the CVD method (CVD-SiN film) has a high defect density and contains hydrogen of the order of 1021 as a quantitative value of the hydrogen by thermal desorption spectroscopy (TDS), improvement thereof is needed.
In addition, since it is difficult to reduce hydrogen by a high film-forming temperature due to the restriction of the film thickness uniformity or step coverage characteristics in the CVD method, a film-forming technique in substitution for the CVD method is required.
In an atomic layer deposition (ALD) method, which may be substituted for the CVD method, a raw material includes hydrogen when an ALD-SiN film is formed using, for example, SiH2Cl2 gas and NH3 gas. Since the hydrogen contained in the raw material remains in the film at a temperature region (about 550° C. or lower) in which the ALD method is performed, a technique to substitute for the ALD-SiN film forming method using SiH2Cl2 gas and NH3 gas, having good film thickness uniformity or step coverage characteristics is needed.
In addition, the SiN film formed by the CVD method is known to have high stress. When the film is directly formed on a silicon substrate, integrational errors such as defects' diffusion into the substrate, an increase in leakage current or an increase in oxidation rate, occur, and thus, stress of the SiN film must be controlled.
[Patent Document 1] Japanese Unexamined Patent Application Publication No. 2003-45864
When a SiN insulating film is formed, hydrogen (H) included in raw materials used when the film is formed remains as impurities in the film due to a low film-forming temperature. Since the hydrogen remaining in the film has a structure such as Si—H bonding or N—H bonding and is easily broken to be a charge trap structure by acceptation and re-bonding of electrons or holes, a defect density may be increased. According to thermal desorption spectroscopy (TDS), since the hydrogen in the film leaves at a film forming temperature or higher, particularly, 800° C. or higher, the hydrogen in the film can be reduced by a high film forming temperature. However, since uniformity of the film thickness in the SiN insulating film is noticeably deteriorated as the film forming temperature is increased, it is difficult to apply this temperature increasing method to production.